The
albedo of a planet or moon tells us how
much of the light that falls on it is
sent back into space.

A scientist asks, "How much of
the radiation that falls on a planet is reflected back out into
space?"The albedo is important because it tells us how much of the
sun's energy actually gets to the surface of the planet or moon.
This affects the planet's temperature.

Most of this radiation comes from the nearest star, but radiation
may also come from other sources. For example, the earth receives
reflected radiation from the moon.

Albedo
is measured between 0
and 1.

A
low albedo planet
absorbs most of the
radiation that falls
on it. It does
not send much of the
radiation back into
space, and so it does
not shine
brightly.

The surface of a low albedo planet is
dark and rough. It may be composed
of dark stones or
solidified lava or a
heavy covering of dark
colored
vegetation.
These kinds of
surfaces absorb tmost
of he radiation that
falls on them.
They soak up heat and
light..

The albedo of such a
world might be 0.02.

If the albedo were
0.02 the planet or
moon would reflect
back only 2% of
the incoming
radiation. Only 2% of the radiation
would be reflected back into space.
Although we think of the radiation as light, it also includes
other radiation, such as infrared rays (heat) and gamma rays
that can kill life
forms

This is a low albedo planet. Notice that
a lot of radiation is going in, and only a little radiation is
being reflected back into space.
This planet could have
a thick atmosphere,
which would tend to
scatter and hold
radiation.

A
high albedo planet or
moon reflects a lot of
light. A
moon with a mirror
surface would reflect
back everything, and
so have an albedo of
one, but it seems
unlikely that there
would be any moons or
planets like
that.

However, some surfaces
are very
reflective.
Clean ice and snow
reflect most of the
radiation that falls
on them. Clouds
can also reflect
incoming light and
heat. For
example, Venus has
dense high clouds that
reflect about 72% of
the radiation that
falls on it. The
clouds are made of
droplets and tiny
crystals of sulfuric
acid. The drops of acid act like tiny mirrors and
send radiation back into space. Venus is the brightest planet
in our solar system with an albedo of
about 72%. It
shines very brightly
in the night sky.
Venus
is a high albedo
planet with an albedo
of .72.

Here you see a high
albedo planet. A
lot of radiation
is
going in, and a lot of
radiation is being
reflected.
Perhaps the radiation
is being reflected by
clouds, as on Venus,
or perhaps the planet
has no atmosphere and
is made of some
light colored
material.

Albedo is not the same all over a world or moon.
On earth, forests have an albedo of about 5%, absorbing much
of the incoming radiation. Ice and snow send most of the radiation
back, and have a high albedo. Scientists
suggest that one result
of global warming will be a melting of the polar ice caps. The
disappearance of these
highly reflective areas will add to the
warming of the planet.